1. Field of the Invention
This invention relates to an electrical inductive apparatus, for example a transformer or reactor, comprising a core and at least one winding wound on the core made from a plurality of superimposed turns of sheet-formed electrically-conducting material. The invention also relates to a method of, and machine for, making an element of the winding.
2. Description of Prior Art
In power transformers and reactors having windings formed from a plurality of turns of sheet-formed electrically-conducting material, a considerable displacement or concentration of the current may occur towards the edges of the turns, resulting in significant additional power loss as well as in considerable localized heating of the sheet at the edges of the turns. From U.S. patent application Ser. No. 176,918 filed in the names of Bertil Moritz et al on Aug. 11, 1980, now U.S. Pat. No. 4,323,870, and assigned with the present application to a common assignee, it is previously known to reduce the current displacement in the turns of the winding by forming the sheet so that the edge regions of at least some of the turns are located at a different distance from the geometrical axis of the winding compared with the distance from said axis of a central conductor portion in a respective one of said turns. The best result is obtained if the winding has a funnel-shaped deflection in the edge regions of at least some of its turns, the distance of the edge regions of such turns from the geometrical axis of the winding being greater than the distance of the central conductor portions of said turns from the geometrical axis of the winding. When using sheet-formed electrically-conducting material of even thickness for the winding turns, a filling material is thus required to bring about the desired funnel-like shape of the winding ends. For dielectric reasons, among other things, it is desirable for this filling to be of an electrically insulating material. Since such filling material has poor thermal conductivity, the filling should be located in thermal symmetry planes, that is, either in the middle of cooling channels passing axially through the winding or midway between two radially spaced-apart, axially extending cooling channels, so that the thermal conduction in the radial direction is not prevented. In the case of windings having cooling channel elements of an advantageous design consisting of a flexible sheet of insulating material having a plurality of grooves for fluid circulation formed in both of its sides (as described in European patent publication No. 40,382 with the present application to a common assignee) it is, however, difficult to arrange separate filling material near the cooling channels in the manner described above. On the whole, the insertion of separate filling presents problems with the location of the filling material, which requires great precision in position. Furthermore such insertion involves manual work resulting in low production rates.
The present invention aims to provide a solution to the above-mentioned problems by the provision in a winding of an electrical inductive apparatus of an element which acts both as a winding shaping member and as a cooling channel defining member.